Would like the ability to apply a highlighter (background yellow, red, etc..) to identify a specific section of code to draw attention to it. Note that this would be inside of the formatted code itself.

That would require changes to the code used to do syntax-coloring right now, which isn't managed by SO. It would be a nice feature though. Perhaps for now your best bet is to show the code without its context, and with its context. It's a bit more verbose than what you're proposing, but it's the best way I can think to achieve this right now.